The present invention generally relates to control apparatuses capable of determining an actuation amount required in controlling a control amount of a controlled object to match a target control amount, and to active sensing apparatuses in which recognition and actuation are performed in a parallel and coordinated manner. More particularly, the present invention relates to a control apparatus which is capable of easily determining an actuation amount with respect to a highly redundant controlled target or a nonlinear controlled target, and to an active sensing apparatus in which the improvement in recognition accuracy and in recognition speed is achieved.
In a control system, there is a process for determining an actuation amount, fed to the controlled target, which is necessary to control the control amount of the controlled target to match a target value. It is necessary that the determination of the actuation amount be done easily with respect to the highly redundant controlled target or the nonlinear controlled target.
Recently, an active sensing method, whereby recognition and action are performed in a parallel and coordinated manner, has drawn attention. In order to make the active sensing method a practical method, it is required that a construction be built whereby the improvement in recognition accuracy and in recognition speed is achieved.
First, a description will be given of a conventional control system.
FIG. 1 is a block diagram showing a generally used feedback control system according to a conventional automatic control theory.
The controlled target in the figure may be an object, a process, a robot or an industrial apparatuses. A detecting part translates the control amount of the controlled target into an appropriate feedback amount that can be compared with the target value. A difference calculator calculates the difference between the feedback amount output from the detecting part and the target value so as to obtain a control deviation. A controlling part generates an actuating signal on the basis of the control deviation calculated by the difference calculator. An actuating part converts an actuating signal generated by the controlling part into the activation amount to be fed to the controlled target.
In a conventional feedback control system having such a construction, the control amount of the controlled target is controlled to match the target value in the following manner: the detecting part detects the control amount of the controlled target and translates the same into the feedback amount; the difference calculating part obtains the control deviation by calculating the difference between the feedback amount and the target value; the controlling part translates the control deviation into the actuating signal; and the actuating part determines the actuation amount to be fed to the controlled target on the basis of the actuating signal so that there is no control deviation. In accordance with this control process, the control amount match the target value with a high precision without being affected by outside influences.
A description will be given of a case in which the above described conventional feedback control technology is applied to the control of a manipulator of a robot. The manipulator control is performed such that the arm tip of the manipulator is controlled to be at a target position by controlling joint angles.
FIG. 2 is a block diagram showing the manipulator control performed when inverse kinematic calculations of the manipulator are performed. An inverse kinematic problem is a problem in which the joint angle and the joint speed for realizing given conditions including the position, orientation and speed of the manipulator. In this case, an inverse kinematic calculation mechanism is provided before a servo-system so that the inverse kinematic calculation mechanism translates a target command relating to the position/orientation of the arm tip into a command relating to the joint angle, thereby effecting a feedback control of the manipulator on the basis of the deviation which takes place between the translated command relating to the joint angle and the observed joint angle.
Since the manipulator currently used in the industry employs a structure in which the inverse kinematic problem can be solved, the control system according to the construction of FIG. 2 is employed therein. The manipulator control as shown in FIG. 3 is employed in the manipulator having a complex structure in which there is no solution to the inverse kinematic problem. In this method, the direct kinematic calculation mechanism translates the joint angle of the manipulator into the position and orientation in the coordinate representation. The deviation which takes place between the command relating to the position/orientation and the observed/translated position and orientation is obtained, whereupon the deviation with respect to the joint angle is generated by applying inverse Jacobian matrix calculations on the obtained deviation, thereby enabling command relating to the angle of each joint of the manipulator to be obtained.
A description will now be given of a conventional sensing technology, and the active sensing technology that has recently come to draw attention.
Generally, a sensing technology is a technology in which the observed target is recognized such that a sensor output indicative of the characteristic of the observed target is obtained by observing the target by means of a detecting part of a visual sensor or the like, a reference is made to the existing knowledge at a recognizing part, and a comparison is made, also at the recognizing part, between the sensor output and the characteristic amount of the observed target. FIG. 4 explains the sensing technology capable of image recognition.
For example, in the field of computer vision, which is extensively studied recently, a two-dimensional image is obtained from a three-dimensional world (observed target) by means of a visual sensor such as a television camera. The sensing of the observed target is reduced to a problem of deducing the state of the three-dimensional world (scene) on the basis of the two-dimensional image. Since the input image is affected by a variety of factors including the camera position, the state of lighting and the configuration/reflectance/relative arrangement of the observed target(s), the characteristic of the scene is deduced by solving an inverse problem of converting the two-dimensional image to the three-dimensional image, wherein the computer is allowed to learn in advance how the observed target will look. However, the inverse problem of converting the two-dimensional image to the three-dimensional image has an infinite number of solutions. In other words, it is a problem characterized by an improper setting in which the unique solution cannot be obtained. Accordingly, the recognition is conventionally performed by assuming a specific lighting condition or a specific reflectance of the object.
With this limitation of the conventional sensing technology as a background, the active sensing technology, in which the sensing of the observed target is executed while a sensor is moved, has come to be studied.
FIG. 5 is a block diagram explaining the active sensing technology. In the active sensing technology, the recognition is not regarded as an isolated task. Instead, recognition and action are executed in a parallel and coordinated manner so as to improve the recognition precision. The sensing is performed such that a sensory perception goal is provided, and an operation for realizing the sensing which achieves that goal is performed. For example, the operation of searching for the target object or the operation of grasping the entire picture of the target object is performed.
FIG. 6 shows an example of how the active sensing technology is realized. In this example, an arm having multiple degrees of freedom is used as a manipulator for executing a measurement action, and a hand camera is used as a visual sensor. In this construction, it is intended that the recognition precision with respect to the observed target is improved by performing a measurement action with respect to the observed target captured by the visual sensor, the measurement action including a searching action, a grasping of the entire picture and a close observation of unclear parts. FIG. 7 is a block diagram explaining the active sensing technology realized in the manner shown in FIG. 6.
According to the conventional feedback control system shown in FIG. 2, there is a need to provide an inverse kinematic calculation mechanism. However, an analytical resolution of an inverse kinematic problem is impossible to obtain in some controlled targets. Hence, there is a problem that a limitation is imposed on the structure of the controlled target. For example, there is a problem that the manipulator is limited to only certain types of structure. There is also a problem in that an inverse kinematic solution is impossible to obtain when there is a redundancy in the degree of freedom of the controlled target or when the controlled target has a nonlinearity.
According to the conventional feedback control system shown in FIG. 3, there is a need to perform inverse Jacobian matrix calculations. Since these inverse matrix calculations consume a large amount of processing time, there is problem that improvement in the speed of control is impossible to achieve. There is also a problem that there are singularities in which an inverse matrix cannot be obtained analytically.
According to the conventional active sensing technology, the algorithm of the measurement action is realized on the basis of human observation of the target and on the basis of human knowledge of the target. In actuality, the algorithm is based on the assumption that the actuator is used only as part of the sensing operation. Hence, the recognition accuracy is not satisfactory. Only the variation, generated by the measurement action, of the sensor signal relating to the observed target is reflected in the sensing, and no element of predictive control is included. Hence, there is a problem of slow recognition.